1. Filed of the Invention
The present invention relates to an optical pickup apparatus for making information record or information reproduction with respect to an optical type information record medium by using a light beam, and particularly to an optical pickup apparatus equipped with a monitor mechanism for controlling the light beam to be proper optical intensity.
2. Description of the Related Art
In an optical pickup apparatus, when a light beam for information record or information reproduction is applied to information record media such as a CD (Compact Disk), a DVD (Video Disk), or the like, optical intensity of the light beam is detected to control driving electric power of a semiconductor laser, which is a light emission source, is performed by an APC circuit (automatic power control circuit), feedback. Also, as a method for detecting the optical intensity of the light beam, a back monitor method has been known.
In this back monitor method, a semiconductor laser for emitting laser beams in two directions backward and forward is used. Then, the laser beam emitted from the forward end of the semiconductor laser is used for information record or information reproduction and the laser beam emitted from the backward end of the semiconductor laser is detected by a photodetector and a detection signal outputted from the photodetector is supplied to the APC circuit and the feedback control is performed so that the driving electric power of the semiconductor laser becomes a predetermined target value and thereby the optical intensity of the light beam applied to the information record media is set to a proper value.
Since the laser beam emitted from the backward end of the bidirectional type semiconductor laser for emitting laser beams in two directions backward and forward is detected directly by the photodetector, the back monitor method has an advantage to be able to simplifying a monitor mechanism. However, when the back monitor method is applied to the use for information record, there was a problem that the APC circuit is greatly influenced by a return beam reflected and returned by the information record media. Therefore, the back monitor method is unsuitable for use as the information record.
The invention overcomes the above described problem. An object of the invention is to provide an optical pickup apparatus comprising a monitor mechanism capable of being applied to both of intensity control of a light beam for information record and intensity control of a light beam for information reproduction wherein the number of parts thereof is small; and miniaturization and weight reduction thereof are enabled.
In order to achieve the object, according to a first aspect of the invention, there is provided an optical pickup apparatus comprising:
a light emission source adapted to emit a light beam;
a control unit for controlling the light emission source to adjust the light beam to a predetermined intensity;
a reflective mirror having a first surface on which the light beam is incident and a second surface, the reflective mirror adapted to reflect the light beam in a direction different from an incident direction of the light beam at a predetermined reflectance and to transmit the light beam to the second surface at a predetermined transmittance; and
a photodetection unit disposed in a second surface direction with respect to the reflective mirror, the photodetection unit adapted to detect the light beam transmitting the reflective mirror,
wherein an information recording medium is disposed in the direction different from the incident direction; and
the control unit controls the light emission source based on a detection output of the photodetection unit.
According to an optical pickup apparatus with such a configuration of the invention, when a light beam for information record or information reproduction is incident from the light emission source to the reflective mirror, the reflective mirror reflects the incident beam to the side of the information record medium at the predetermined reflectance and transmits the light beam to the side of the photodetection unit provided in the second surface direction at a predetermined transmittance. Then, on the basis of the detection output of the photodetection unit, the control unit controls the light emission source so as to adjust the light beam for the information record or information reproduction to the proper intensity.
Therefore, any light beams for the information record and the information reproduction can be detected by one photodetection unit, and the invention can realize the optical pickup apparatus with the above described structure capable of, for example, a reduction in the number of parts, miniaturization of apparatus scale and weight reduction and also, on the basis of the detection output of the photodetection unit, APC control of the light emission source can be performed so that any light beams for the information record and the information reproduction become the proper intensity.
Also, in order to achieve the object, according to a second aspect of the invention, there is provided an optical pickup apparatus comprising:
a light emission source adapted to emit a light beam;
a control unit for controlling the light emission source to adjust the light beam to a predetermined intensity;
a reflective mirror having a first surface on which the light beam is incident and a second surface, the reflective mirror adapted to reflect the light beam in a direction different from an incident direction of the light beam at a predetermined reflectance and to transmit the light beam to the second surface at a predetermined transmittance; and
a photodetection unit disposed in the direction, the photodetection unit adapted to detect the light beam reflected by the reflective mirror,
wherein an information medium is disposed in a second surface direction with respect to the reflective mirror; and the control unit controls the light emission source based on a detection output of the photodetection unit.
According to the optical pickup apparatus with the above described configuration of the invention, when the light beam for information record or information reproduction is incident from the light emission source to the reflective mirror, the reflective mirror transmits the incident beam to the side of the information record medium located in the second surface direction at a predetermined transmittance. Further, the light beam is reflected to the direction, which is the side of the photodetection unit, at the predetermined reflectance.
Therefore, any light beams for the information record and the information reproduction can be detected by one photodetection unit, and the invention realize the optical pickup apparatus with the above described structure capable of, for example, a reduction in the number of parts, miniaturization of apparatus scale and weight reduction and also, on the basis of the detection output of the photodetection unit, APC control of the light emission source can be performed so that any light beams for the information record and the information reproduction become the proper intensity.
Also, in order to achieve the object, according to a third aspect of the invention, there is provided the optical pickup apparatus according to any one of the first and second aspects,
wherein the reflective mirror has a transparent medium;
the first and second surfaces are not parallel to each other; and
one of the first and second surfaces has a semi-transmission film having the predetermined reflectance and the predetermined transmittance.
According to an optical pickup apparatus with the above described configuration of the invention, a multiple reflected light beam occurring in case that the light beam for the information record or information reproduction is incident to the semi-transmission film of the reflective mirror can be reduced so as not to reach the side of the information record medium and the side of the photodetection unit. That is, by the surfaces, which are not parallel to each other, the multiple reflected light beam is reflected and transmitted in a direction deviating from an optical path. As a result of that, an influence of the multiple reflected light beam can be reduced to perform photodetection necessary to control the light emission source, and the light emission intensity of the light emission source can be controlled with high accuracy.